Conicgraph



T. S. SAJATOVICH Feb. 16, 1954 CONICGRAPH 4 Sheets-Sheet 1 Filed June 25, 1949 I INVENTOR. mamas s. SAJJHTOVICH BY 1954 T. s. SAJATOVICH 2,669,022

CON ICGRAPH Filed June 25. 1949 4 Sheets-Sheet 2 INVENTOR.

THOMAS a 6HJKI'OVICH awa Feb. 16, 1954 T. VS. SAJATOVICH CONICGRAP'H 4 Sheets-Sheet 5 Filed June 25, 1949 INVENTOR. THOMAS s. SAJHTOVCH BY 2 l Feb. 16, 1954 s, SAJATOVICH 2,669,022

CONICGRAPH I Filed June 25, 1949 4 Sheets-Sheet 4 INVENTOR.

THOMAS 5. SHJATOVICH Patented Feb. 16, 1954 OFFICE 2,669,022 7 bonroenA rn Thomas SgSajajtovicb, Cleveland, Ohio Application June 25, 1949, Serial No. 101,319

(slice- 27) This invention relates to an improvementin I conicgraphs and, more particularly to a drafting instrument which permits the scribing of mathematically precise sectionsfi o o Heretofore the precise scribing of hyperbolas and parabolas of mathematically correct curvatures for the. focus, center, and vertex of the curves has presented an extremely difiicult problem in designing and production drafting and has hyperbolic and parabolic conic required advanced mathematical computations far beyond the capabilities of most graduate engineers, let alone the capabilitiesof skilled design and production draftsmen. The scribing of a parabola is actually merely tedious rather than diificult, sinceit-involves merely the location of points equidistant from a focus and a 'directrix, the location and direction of the directrix following from the two determining points, the focus and vertex, since but one parabola may exist for a given vertex and a given focus. The scribing of a given hyperbola, however, is considerably more diflicult since an infinite number of hyperbolas may have the same vertex and focus, three points, vertex, focus, and center, determining a given hyperbola. It was generally prior practice to determine a few of the points on the desired curve and then fair 'in the curve from these points with a French "invention'to provide a conic section drafting instrument which will, in the case of a parabola, permit the curve to be quickly and easily scribed,

the vertex and focus being known, or, but one of.

these'pointsbeing known, the other point may be arbitrarily selected, as good design or proportion "may dictate, andthecorresponding curve may be selected; In the case of a hyperbola with a known vertex, focus and center, the instrument may be set to these points and the resultant curve scribed, or if only two of these points are known or selected, the instrument may be operated. to scribe a true hyperbola, the third point then being locatable from the curve by means .of the instrument.

.,.Another object and advantage of, my invention :is, to provide, a. novel scriber for pen or pencil vwhichwvill be rmal. to. t p a e .of the cur v n);alumni within the. odimensipnalilim ts of th 2 instrument, thereby avoiding inaccuracies caused by efforts to maintain the scriber at an operative scribing angle throughout the movement of the scribing arm. Another object of my invention is to provide a novel bearing permitting relatively frictionless longitudinal and rotational movement of the scribing arm while the curve is being scribed. These subcombinations .are useful in all types of conicgraphic instruments, including ellipsographs as well as instruments for scribing hyperbolas and parabolas. In fact, employment of these subcombinations in known types of ellipsogra'phs render such instruments, othering specification, the claims, and the drawings showing a preferred embodiment of my invention, in which Fig.1 is a side elevation of the instrument arranged for drafting a hyperbola.

Fig. 2 is a plan view of the instrument as shown in Fig. 1, but partly broken away and with the scribing arm swung to a position assumed in scribing the hyperbola shown.

Fig. 3 is an elevation of the other side of the instrument shown in Fig. 1, but with the instrument arranged for scribing a parabola;

Fig. 4 is a detail cross-section of the pencil scriber (without lead and quadrant) taken along the line 4-4 of Fig. 3. r

Fig. 5 is a detail side elevation of the scriber shown in section in Fig. 4.

Fig. 6 is a modification of the scriber shown in Fig. 5, said modification carrying an ink pen.

, Fig. 7 is a detail cross-section of the scriber arm bearing.

Fig. 8 is a detail of the bearing sleeve shown in section in Fig. 7. v

For purpose of definition and explanation of ,the principle of my instrument, it should be borne in mind thata parabola is the curve defined by a plane intersecting a coneowhere the plane is parallel to an element of the cone; a hyperbola is the curve vdefined by a plane intersecting a cone where the plane is parallel to the axis of the cone.

My instrument is based on the mathematical principle that for either a parabola or a hyperbola there maybe constructed within the cone a sphere which is tangent to the cone and to the intersecting plane at the focus of the curve. Since the center of ahyperbola is, by definition, th pmi tiqn of t e p x cf the co e pcn the intersecting plane, the vertex of the curve is the point defined by the element of the cone which intersects the line between the center and the focus. In a parabola the vertex is simply the point on the curve nearest the focus, and, thus, is the point located by the intersection of the intersecting plane and the shortest element of the intersected cone.

As shown in Figure 1, arranged for scribing a hyperbola, my instrument comprises a base Iii having a focus point I adapted to be set on the focus F of the intersecting plane IP (usually the sheet of paper, metal, or the like upon which the hyperbola is to be scribed). provided with outrigger points 12 tostabilize it.

Extending perpendicularly above the'baselii is The base- 1d. is

a center post It carrying the "vertically slidable center bearing M on which is pivoted the axial bearing l5, the post |3being offset with respect I beingtwisted out of alignmentwith the'focus 1 point, the center bearing Hi and the post |3 are preferably providedwith mating flats, against -whioh the set screw IE'may bear in'order tow maintain the center'bearing at the desired-elevation.

'The angularity of the pivoted axial bearing I5 with respectto the center-bearing may be set by means of the center uadrant arm ll ca-rrled'by the bearing-"Hand the set screw i8 carried by the bearing I5; In Fig. 1 the axial bearing I5 is set at rightangles to the bearing M so that the-axis rod 2!),slidablyjournaled in the bearing l5 and representing theaxis of the intersectedcone, maybe parallel to the intersecting plane IP, as is necessary "by definition of the hyperbola to be scribed. The axisyrod '20 may be fixedin the bearing l5 by--means of theset'screw I9.

One end of the rodZil carries apilotishaft 2| on which is freely rotatably-mounted the apex fork bearing 22-carrying the apex fork 23, in which is pivoted the scriber -or element-arm bearing 24; The-scriber; arm 25 is slidablyand rotatably journaled in the bearing-2t, the intersection of the center line of the axis rod and the center line of the scriber arm representing the apex of the intersected cone. The

angularity of the scriber armbearing 24-with respect to the axis rod 20 is adjustabl y fixed by means of the apex quadrant 26 carried by the fork 23 and the set screw 2'! carried by the'bearing 24. With the angularity of the scriber arm s0 fixedQwhen the fork 23 is rotated on the pilot shaft 2|, the scriber arm 25 thus. generates'a" cone about the axis rod 20 and"'wherever the c'enter'line of' the scriber' arm intersects" the plane 1P, therefore, the locus of the points of intersection will bea hyperbola.

To permit a curve to be scribed along the locus of points of intersection of the c'e'nterline 'of the scriber arm 25 and the plane IF, the end of the arm 25 carries a rotatably mounted scriber quadrant "3 0 provided with an arcuate slot"3| concentric about a point'on the extended center line "of the arm 25. As shown in Figs. '4 and 5, a scriber' 324s providediand comprises a block provided with an arcuate boss 33" adapted 'to*slide-in the slot 3|." The boss' 33 "is tapped "to receive a set 's'crew' '34 so that the radi'al position of the scriber 32 in the quadrant 38 may be adjusted. The lower end of the scriber is drilled radially to provide a receiving socket 36 for a lead 35 and is slit to provide jaws 3! which may be closed by a thumbscrew 38 to grip the lead 35. In use, a sharpened lead is adjusted in the jaws 31 so that distance from the point of the lead to the set-screw 34 is equal to the radius of the slot 3|. The point of the lead 35 thus coincides with the intersection -of the center line of the quadrant arm zii'an'd the plane LP. By selecting a suitable angle for the scriber 32 the quadrant 38, lead will be at the proper '1 angle to scribe a sharp line throughout most hyperbolas. If the hyperbola is large or so sharply curved that the angle of the lead to they-plane changes appreciably in scribing the hyperbola, the angle of the scriber in the quadraht-inay be changed while the hyperbole. is being scribed Withoutiafiecting the accuracy of the'curve.

A sharpened scribing'point instead' 'offa ilead 35 may be used in the-"s'cribe'rBZ if thec'urve 'is to be scribed on metal, for example. IE it is desired to scribe the hyperbola in ink,ia'rotat- 'able pen-equipped scriberstz, as shown win Fig.

6, may be substituted. 7

As thelcurve is scribed, it is: evident that the scriber arm 25 will'move 'longitudinall-yin the bearing 24 and, in'order to maintain the scriber in a vertical position, the arm v25'will-=-also :be turned. Such movement should-be substantially frictionless and yet the arm'-25 must--be: accurately centered inthe-bearing. To accomplish such frictionless coaxial movement :ofthe arm 25 in the bearing 24, thebeari-ng;Mdscomprisedofa shell Ml carryinga sleeve 4|. --:The ends of the sleeve are ringed withballopenings 42 and additional -ball openings 42 are located helically around the sleeve between-"the; end

openings, as shownin Fig. 8.- Ballbearings 43 center the arm 25 precisely coaxially in-the shell lll, being spaced'from-each other-bythe sleeve 4|. Itshould be not'edthat the. diameter ofthe. ball openings-42 is slightly less than the diameter of the balls '43- andthat the. radius of the sleeve H is slightlyless .thanthe distance from the center of theballs -43 to the-axis of the arm 25.- Thus, the balls are'reta'ined (in the bearingv 24 even though the arm 25 may be removed therefrom. .The sleeve 4| is 'heldlin the shell 4|] by means ofthecap 46.

If the definite hyperbolaflmiis't'bescribEd for "a'lmo'wn focus, vertex and center, theradiusarm 5B mustbe'e'mployed. The radius arm 50. islslidably journaled in the bearing 5| pivoted. on the center bearing M concentrically with..the. axial bearing H3. The lower endof theradiusann' 50 is provided with an offset foot 52 -adapted filofit "over the scriber arm '25, the foot 52 being a't'right angles to the arm 5%. The arm fidearrie's 'a'pivot nut 53 and a second oppositely .th'readedipivot nut 54 iscarriedby the centerpost |3, th e perpendicular distance from the center line -of the scriber-arm 25 to the pivot nut 53-beingequalto the distance from the focus-p0 l t-| to the pivot sitely threaded endsof the bisector-screw 55 which is carried by the forked bisectOrarm-"BB. The forked end of .the 'bisector" armi'islocated equidistant between the nuts 53 and ifi andwis on the centerb'earing M concentrically with the to-u the radius of the aforesaid constructed sphere. j

.With the focuspoint' l I set on the focus F and the effective length of the axis rod set to the distance between F'and the center C, the altitude of the center bearing I4 is adjusted until the scriber points may be set on the known vertex V and the radius arm 55 is perpendicular to the scriber arm, 25,- as' shown in Fig. [1. In this position, the center line of the scriber arm is equivalent to the element of a cone tangent to a constructed' sphere which, in turn, is cotangent with the intersected cone and the intersecting plane. Toscribe th hyperbola determined by known fpoints F; V, and C, the radius arm 501is simply swung to a dotted line position as shown in -Fig'. 1'

and the hyperbola is scribed by swinging the scribing arm 25, as indicated in Fig. 2. It should also be evident that, by adjustingimy instrument as for soribinga, hyperbola to the three known determining points, my instrument in'ay'also be used to locate one 'of the unknown points if the center, focus, or vertex of a scribed hyperbola is unknown; this use of the instrument ,can sav econsiderable calculation when either the focus" or center is unknown, for an unknown vertex is located by simply'noting the intersection of the curve with the line between focus and center. Indeed, if the hyperbola is large enough to permit the asymptotes to be located, the instrument permits the location of the focus to be accomplished without calculation; the center being determined by the intersection of the asymptotes, the nearest point on the curve is the vertex; then by holding the scriber on the vertex, the length of the axis rod and th elevation of the center are adjusted while maintaining the radius arm perpendicular to the scriber arm. When the apex point is perpendicularly above the center, the point I l marks the focus.

scribing a parabola To scribe a parabola with a known focus and vertex, the axis rod 20, which, surprisingly, may be of any arbitrary length convenient for the dimensional limitation of the other elements of the instrument, is adjusted in the axial bearing I5 so that the center line of the bearing pivot intersects the mid-point of the length of the rod between the apex point in the fork 23 and the point of the center line pin 29. Maintaining the point of the pin 29 on the plane IP, the pin H on the focus F and the scriber point on the vertex Vp, the center block 14 is elevated and the radius arm 50 is adjusted until the radius arm foot 52 is perpendicular to the scriber arm 25, as shown in Fig. 3. The angularity of the axis rod 20 with respect to the post I3 and the scriber arm bearing with respect to the fork 23 are then set by setting the appropriate quadrant set screws. The parabola is then scribed by swinging the scriber arm about the axis rod while maintaining the scriber in contact with the plane IF, the radius arm being swung out of the way while the parabola is being scribed. That a mathematically precise parabola is scribed is evident from the fact that if the scriber arm 25 were swung until it was vertically above the axis rod 20, the center line of the radius rod, as indicated by the construction line 6p, would be necessarily and geometrically parallel to the plane IP. The swinging movement of the scriber arm about the axis rod, therefore, generates a cone having an element e parallel to th intersecting plane IP, and the scriber arm 25, accordingly, by moving longitudinally in the bearing 24, marks the locus of .1' If,.as'is often the case, only the desired loca-.

tion of the focus or vertex is known, the instrument, with the radius arm perpendicular to the scriber arm as shown in Fig. 3, may be set at arbitrary, distances between the focus and vertex until a parabola ,of the desired size and configuration is scribed. I'his invention is not limited to the particular mechanisms for effecting-the desired movement of the elements of the instrument with respect to each other,as. are shown in the preferred embodiment disclosed. The preferred embodiment maybe modified in whole or in part by those skilled in the art without departing from the scope of the invention as defined in the following claims.

mWhat is claimed is: v I I 1.-A conicgraph for scribing parabolas and hyperbolas comprisinga base structure having a focuspoint, a main bearing member, a support for said main bearing member carried by said base, an axis rod, means slidably and pivotally supporting said axis rod ,in said main bearing member perpendicularly above said focus point, the perpendicular abovesaid focus point and the axis of said rod intersecting to constitute a first intersection, a scriber arm, means pivotally mounted on one end of said axis rod and rotatably and slidably carrying said scriber arm, the axis of said scriber arm and the axis of said rod intersecting to constitute a second intersection, a scriber carried by said scriber arm and having a scribing point falling on the axis of said arm, means to locate the axis of said scriber arm tangent to a circle lying in the plane defined by said perpendicular and the axis of said rod, said circle being centered on said first intersection and having a radius equal to the distance from said focu point to said first intersection and adjustabl means to fix the angles of intersection at said first and second intersections.

2. A conicgraph as defined in claim 1 in which said means to locate the axis of said scriber arm tangent to said circle comprises a radius arm, means for slidably supporting said radius arm pivotally concentrically about said first intersection, a foot carried by said radius arm and extending perpendicularly thereto, said foot being adapted to engage said scriber arm and locate said radius arm perpendicular thereto when said scriber arm is in the plane of said circle, a first pivot bearing carried by said support for said main bearing, and a second pivot bearing carried by said radius arm, the distance from the pivoted axis of said first pivot bearing to the focus point being equal to the distance from the pivotal axis of said second pivot bearing to the axis of said scriber arm when said foot engages said scriber arm, a link extending between said pivot bearings and movable axially therein, and means for maintaining the angle between said link and said main bearing support equal to the angle between said link and said radius arm.

3. A conicgraph as defined in claim 2 in which said link comprises a turn buckle screw threaded in said pivot bearings and said means for maintaining equal angles between said screw and said radius arm comprises a bisector arm in which said turn buckle screw is journaled at its midpoint and perpendicularly to said bisector arm, and a bearing in which said bisector arm is slidably journaled, said bisector arm bearing being swam 7 pivoted zconcentricallyw witmssaidi first intersecr tion.

42 A- conicgraphgastdefinemin claim 1 in awhioh said meansnpivotally mounted omsaidmaxisa'od and rotatably: and shimmy-carrying said? scriber arm comprises a fork rotatably momrtedala;about the: axis of said axis= r od anct a bearing pivoted inthe't-inesof said fork about awpivotal axis-1mtersecting the axis Of said axisroduanduthe axis of-- said: bearing at a oommon-rpointsaida bearing comprising a casing: =-ha=ving a cy1indrd'ca1:=bore,- a concentricretaining -s1eeve within". said c'asing a plurality of ballopenings in said retaining: sleeve distributed --a1o'ng 'therlength thereof-, and' a 13111- rality of balls rhounteddmsaid openings;the 'c1i-- am'eter of said=- bal-l-openi-ngs being less thana the diameterof said: balls and the inner diameter of said casing, the outer diameter of said sleeve; the diameter of said ball openings and-the thickness of "said: sleeve being proportioned? -to :maintain 20 said balls between said sleeve and casing while permitting said balls to extend through: "s'aidball openings-When said-balls are in contact with the inner diameter 01% Said. casing whereby; :When a scribe!" arm-,- having a diameter equal tothe inner diameterofsaid casing lesstwiceth diameter of said ba11s5-is journale'd in said ballsg said-scriber arzmzzvwmz ibemccaxiatly rotatablyrs and slidably mounted in said casing.

. THOMASIS. 'SAJATQWCH.

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gFrizell'; fThe Conic- Section Compasses, The 

